Believe It? A Material That Can Run In Reverse

MINNEAPOLIS — Physicists have popped through the looking glass and created a new material in which fundamental laws of nature apparently will run in reverse.

Just as Alice in Wonderland found a world where everything was curiouser and curiouser, this stuff behaves in ways that are "reverser and reverser," said Dr. Sheldon Schultz of the University of California, San Diego, in whose lab the research was done.

The material has properties never before reported in natural or artificial substances. These properties could cause microwaves to bounce through the material in completely opposite directions from how they would in ordinary materials. Such behavior would reverse, but not break, a physical law.

The possibility of such a material's existence was predicted more than 30 years ago.

The work might one day lead to faster and better cellular phones, which rely on microwave transmissions. Or there may be entirely new types of applications that cannot even be imagined today, scientists said.

"Someone's got to think of something clever to do with this," Schultz said Tuesday in Minneapolis, where he announced the finding at a meeting of the American Physical Society.

The material is made of nothing fancy. It's a palm-sized array of small copper rings hung between a grid of copper rods. It is the arrangement of the rings and rods that creates the bizarre new behavior, which so far has been demonstrated only with microwaves but potentially could work in other electromagnetic wavelengths.

If the stuff plays similar tricks with visible light waves -- which hasn't been tested and might not be possible -- it could grow curiouser yet, said David Smith, the other leader of the San Diego team. For instance, Snell's law, a scientific description of how rays bend through different materials, would run in reverse: A lens made of this material would scatter, rather than focus, light.

Other physicists called the discovery exciting and potentially very important.

"Technology is hungry for new materials, and what is on offer here are totally new materials, most of which have no counterpart in nature," wrote John Pendry, a physicist at Imperial College in London, in an e-mail interview.

During the past few years, Pendry developed the foundation for the San Diego team's work. For example, he was the first to use copper rings and rods, although separately, to alter two specific electrical and magnetic properties of a material.

A series of copper ring pairs, each of which looks like one locking washer set inside another, exhibits a reversed version of the property called magnetic permeability, which describes how the material responds to a magnetic field. Instead of being a positive number as it is for most materials, the rings have a negative magnetic permeability.

Similarly, using an array of copper rods switches a property called electric permittivity, which describes how the material responds to an electric field. The rods turn out to have negative electric permittivity -- again, rather than positive, Pendry noted.

The San Diego team put rings and rods together for the first time, creating a material with both negative magnetic permeability and negative electric permittivity. Such a combination of properties, which should cause the reversal of physical laws, had never been created before, the scientists write in an article to appear in the journal Physical Review Letters.